Recent reports have suggested that persons who are exposed to electric and magnetic fields either occupationally or by living near power lines are at increased risk of leukemia, particularly acute myeloid leukemia. This study is an epidemiologic case-control investigation of the risk of acute myeloid leukemia in telephone linemen, a group of workers exposed to power distribution lines and identified as being at risk in the work of other investigators. Through an arrangement with the Medical Research Department at American Telephone & Telegraph we have identified all deaths from acute myeloid leukemia that occurred in active or retired telephone company employees between 1975 and 1980 from their computerized mortality data base. The death certificate diagnosis of these cases is being validated through a review of company medical records. A matched control group is being selected from the Bell System personnel data base comparable to the cases in age, sex, race and calendar time of employment. Complete work histories for the study subjects will be obtained from telephone company personnel service record cards. Onsite visits are being conducted to ascertain exact job titles and describe the job activities associated with line work and exposure to electric and magnetic fields. Actual field measurements using available meters are planned. Telephone company jobs will then be classified by degree of exposure to electric and magnetic fields. In the analysis we will determine the odds ratio of having ever been a lineman among the acute myeloid leukemia patients compared to the controls, and the degree of association of disease with field exposure.